JP2005061362A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of improving NOx reduction efficiency. <P>SOLUTION: In this exhaust emission control device, a NOx reduction catalyst 1 is installed in a flowing passage 11 for exhaust G sent from an engine 6. An addition nozzle 22 to mix urea water U to the exhaust G is installed on an exhaust manifold 7 of the engine 6 to be positioned at a turbo charger 8 close to an inlet to a turbine 9. Urea water U for reduction is added to high-temperature exhaust on the upstream side of the turbo charger 8 in an advance direction of exhaust G, so that the exhaust to rotate the turbine 9 is mixed with fine drops of urea water U. Decomposition of urea water U is thus accelerated to secure generation quantity of ammonia. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust purification device.

  In recent years, there has been an exhaust purification device that incorporates a urea selective reduction catalyst capable of selectively reacting with a reducing agent even in the presence of oxygen in the exhaust system of a diesel engine so as to reduce the NOx concentration in the engine exhaust. It has been proposed (see, for example, Patent Document 1).

  As shown in FIG. 6, this exhaust purification apparatus includes a urea selective reduction catalyst 1 and an ammonia oxidation catalyst 2 that are arranged in order from the upstream side to the downstream side in the traveling direction of the exhaust G to be purified, and the reduction catalyst 1 and the oxidation catalyst. A casing 3 that houses the catalyst 2, an addition nozzle 4 that sprays urea water U onto the exhaust G, and an arithmetic unit 5 are provided.

  As the reduction catalyst 1, one composed of an oxide such as vanadium, titanium, tungsten, one composed of copper, zeolite, or zeolite is used.

  As the oxidation catalyst 2, a material having a physical property capable of generating ammonia or nitrogen monoxide by oxidizing ammonia is used.

  The casing 3 is provided in an intermediate portion of the exhaust gas distribution path 11 from the exhaust manifold 7 of the engine 6 through the turbine 9 of the turbocharger 8 to the muffler 10.

  The addition nozzle 4 is attached in the vicinity of the exhaust inlet of the casing 3 so as to be located upstream of the reduction catalyst 1 in the traveling direction of the exhaust G.

  A pump 15 that is driven by a motor 13 that receives power from the control unit 12 and that sucks and discharges urea water U from a tank 14 is connected to the addition nozzle 4 via an electromagnetic valve 16.

  A NOx concentration sensor 28 is provided upstream of the addition nozzle 4, a temperature sensor 17 is provided in the vicinity of the exhaust inlet of the casing 3, and a NOx concentration sensor 18 is provided in the vicinity of the exhaust outlet of the casing 3. A temperature sensor 29 is provided.

  In addition, the engine 6 is accompanied by a rotation speed sensor 19, and the accelerator pedal 20 is accompanied by an accelerator sensor 21 that calculates a load command based on the depression angle.

The arithmetic unit 5 is
a. A function for calculating a predicted amount of NOx generated assuming the current operating state of the engine 6 from the rotational speed of the engine 6 obtained by the rotational speed sensor 19 and the load command value for the engine 6 obtained by the accelerator sensor 21;
b. A function of calculating the amount of urea water U added in accordance with the expected generation amount;
c. When the ambient temperature near the exhaust inlet or exhaust outlet of the casing 3 obtained by the temperature sensors 17 and 29 is included in the activation temperature range of the reduction catalyst 1, the solenoid is excited to open and control the solenoid valve 16. A function of operating the motor 13 by the unit 12 to drive the pump 15 and spraying the urea water U to the flow of the exhaust G from the addition nozzle 4 based on the addition amount;
d. A function of correcting the addition amount of urea water U according to the NOx concentration near the exhaust outlet of the casing 3 obtained by the NOx concentration sensor 18 or the NOx concentration near the upstream of the addition nozzle 4 obtained by the NOx concentration sensor 18;
Etc.

That is, when the temperature of the exhaust gas G is included in the activation temperature range of the reduction catalyst 1, when the urea water U as a reducing agent is added to the exhaust gas G, the urea water U is first decomposed into ammonia and carbon dioxide.
[Chemical 1]
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂

Next, NOx in the exhaust G is reduced by the reduction catalyst 1 and ammonia, and the release of NOx into the atmosphere is suppressed.
[Chemical 2]
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O
[Chemical formula 3]
6NO + 4NH ₃ → 5N ₂ + 6H ₂ O
[Chemical formula 4]
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O

Furthermore, even if a small amount of ammonia passes through the reduction catalyst 1 without being reacted, the ammonia is oxidized by the oxidation catalyst 2 and nitrogen or nitric oxide is released into the atmosphere.
JP 2002-161732 A

  However, in the exhaust emission control device shown in FIG. 6, immediately after the engine 6 is started, the exhaust inlet of the casing 3 (exhaust G progress of the reduction catalyst 1 proceeds due to operation in a cold region of the vehicle, continuation of low load operation of the engine 6, etc. (Upstream in the direction) and the exhaust outlet (downstream in the direction of exhaust G travel of the reduction catalyst 1) does not become high (specifically, it does not exceed 200 ° C.), urea water sprayed from the addition nozzle 4 U becomes difficult to decompose, and therefore, the amount of ammonia produced is insufficient and NOx cannot be reduced efficiently.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an exhaust purification device capable of improving NOx reduction efficiency.

  In order to achieve the above object, the invention described in claim 1 is directed to an exhaust gas purification apparatus in which a NOx reduction catalyst is installed in a flow path of exhaust gas sent from an engine, and a reducing agent adding means for mixing urea water in the exhaust gas. It is installed so that it is located upstream of the turbocharger attached to the engine in the exhaust traveling direction.

  According to the second aspect of the present invention, in the exhaust gas purification apparatus in which the NOx reduction catalyst is installed in the flow path of the exhaust gas sent from the engine, the reducing agent addition means for mixing urea water in the exhaust gas is more advanced than the reduction catalyst. A heating means is provided so as to be located upstream in the direction, and raises the temperature of urea water to be supplied to the reducing agent addition means.

  According to a third aspect of the present invention, there is provided an exhaust gas purification apparatus in which a NOx reduction catalyst is installed in a flow path of exhaust gas delivered from an engine, and a reducing agent addition means for mixing urea water in the exhaust gas is provided with a turbocharger attached to the engine. The heating means is provided so as to be located on the upstream side in the exhaust traveling direction and raise the temperature of the urea water to be supplied to the reducing agent addition means.

  According to a fourth aspect of the present invention, an ammonia oxidation catalyst carrying a zeolite and a noble metal catalyst is installed on the downstream side of the NOx reduction catalyst.

  In the first aspect of the invention, the urea water for reduction treatment is added to the high-temperature exhaust gas upstream of the turbocharger in the exhaust traveling direction, and the exhaust gas for rotating the turbocharger and the fine droplets of urea water are mixed. , And promote the decomposition of urea water to ensure the production amount of ammonia.

  According to the second aspect of the present invention, the urea water for reduction treatment to be added to the exhaust gas is heated by the heating means to promote the decomposition of the urea water to secure the amount of ammonia generated.

  In the invention according to claim 3, after the urea water for reduction treatment to be added to the exhaust gas is heated by the heating means, the urea water is added to the high-temperature exhaust gas upstream of the turbocharger in the exhaust traveling direction. The exhaust gas that rotates the turbocharger and the fine droplets of urea water are mixed together to promote the decomposition of the urea water to secure the amount of ammonia produced.

  In the invention according to claim 4, ammonia that has not contributed to the reduction of NOx is oxidized to nitrogen or nitric oxide by the zeolite and the noble metal catalyst.

  According to the exhaust emission control device of the present invention, the following various excellent effects can be obtained.

  (1) In the first aspect of the present invention, the exhaust gas for rotating the turbocharger and the fine solution of urea water are added by adding urea water for reduction treatment to the high-temperature exhaust gas upstream of the turbocharger in the exhaust traveling direction. Since the droplets are mixed and the decomposition of the urea water is promoted, the amount of ammonia produced can be secured, and the NOx reduction efficiency is improved.

  (2) In the invention described in claim 2, the temperature of the urea water for reduction treatment to be added to the exhaust gas is raised by the heating means to promote the decomposition of the urea water. And NOx reduction efficiency is improved.

  (3) In the invention described in claim 3, after the temperature of the urea water for reduction treatment to be added to the exhaust gas is raised by the heating means, the urea water is added to the hot exhaust gas upstream of the turbocharger in the exhaust traveling direction. Is added, and the exhaust gas for rotating the turbocharger and the fine droplets of urea water are mixed to promote decomposition of urea water, so that the amount of ammonia generated can be ensured and the NOx reduction efficiency is improved.

  (4) In the invention described in claim 4, since the zeolite and the noble metal catalyst are supported on the ammonia oxidation catalyst, the remaining ammonia that has not contributed to the reduction of NOx is efficiently oxidized to nitrogen or nitric oxide. can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a first example of an embodiment of an exhaust emission control device according to the present invention. In the figure, the same reference numerals as those in FIG. 6 denote the same components.

  This exhaust purification device replaces the above-described addition nozzle 4, calculation unit 5, and NOx concentration sensor 28 (see FIG. 6), an addition nozzle 22 for spraying urea water U, a calculation unit 23, and exhaust from the engine 6. And a NOx concentration sensor 30 provided in the manifold 7.

  Further, as the oxidation catalyst 2, a honeycomb structured cordierite carrier having an acidic substance such as zeolite (silica / alumina material) and a noble metal catalyst (platinum, palladium, or both) supported thereon is used. Yes.

  The addition nozzle 22 is attached to the exhaust manifold 7 so as to be positioned near the exhaust inlet of the turbocharger 8 (turbine 9).

  A pump 15 is connected to the addition nozzle 22 via an electromagnetic valve 16.

The arithmetic unit 23 is
a. A function for calculating a predicted amount of NOx generated assuming the current operating state of the engine 6 from the rotational speed of the engine 6 obtained by the rotational speed sensor 19 and the load command value for the engine 6 obtained by the accelerator sensor 21;
b. A function of calculating the amount of urea water U added in accordance with the expected generation amount;
c. When the expected generation amount exceeds a preset threshold value, the solenoid is excited to open the solenoid valve 16 and the motor 13 is operated by the control unit 12 to drive the pump 15 and exhaust from the addition nozzle 22. The function of spraying urea water U against the flow of G,
d. A function of correcting the addition amount of urea water U according to the NOx concentration near the exhaust outlet of the casing 3 obtained by the NOx concentration sensor 18 or the NOx concentration in the exhaust manifold 7 obtained by the NOx concentration sensor 30;
Etc.

  That is, the urea water U used for the NOx reduction treatment is sprayed on the high-temperature exhaust G immediately after being discharged from the cylinder of the engine 6, and when the exhaust G rotates the turbine 9, the urea Decomposition of urea water is promoted by a synergistic effect of the mixing of fine droplets of water U and exhaust G.

  That is, in the exhaust emission control device shown in FIG. 1, immediately after the engine 6 is started, the exhaust inlet of the casing 3 (exhaust G progress of the reduction catalyst 1 progresses by operating the vehicle in a cold region, continuing the low load operation of the engine 6, etc. Even when the ambient temperature on the upstream side in the direction does not increase, the amount of ammonia produced is ensured, and NOx contained in the exhaust G can be reduced efficiently.

  The relationship between the atmospheric temperature of the reduction catalyst 1 and the NOx reduction rate of the exhaust G in this embodiment has a tendency as shown by a solid line in FIG. 2, and the atmospheric temperature of the reduction catalyst 1 in the conventional example of FIG. The relationship with the NOx reduction rate has a tendency as shown by a broken line in FIG.

  Further, even if a small amount of ammonia passes through the reduction catalyst 1 without being reacted, the ammonia is oxidized by the oxidation catalyst 2 and nitrogen or nitric oxide is released into the atmosphere.

  FIG. 3 shows a second example of the embodiment of the exhaust emission control device of the present invention. In the figure, the same reference numerals as those in FIG. 6 denote the same components.

  This exhaust purification apparatus includes a heater 24 and a calculation unit 25 instead of the calculation unit 5 (see FIG. 6).

  The heater 24 has a heating wire 27 that receives power from the control unit 26 and raises the temperature of the urea water U to be delivered toward the addition nozzle 4.

The arithmetic unit 25 is
a. A function for calculating a predicted amount of NOx generated assuming the current operating state of the engine 6 from the rotational speed of the engine 6 obtained by the rotational speed sensor 19 and the load command value for the engine 6 obtained by the accelerator sensor 21;
b. A function of calculating the amount of urea water U added in accordance with the expected generation amount;
c. When the ambient temperature near the exhaust inlet or exhaust outlet of the casing 3 obtained by the temperature sensors 17 and 29 is lowered to about 200 ° C., the control unit 26 causes the heating wire 27 to be overheated, A function of raising the temperature of the urea water U to be sprayed to at least 150 to 200 ° C .;
d. When the predicted generation amount exceeds a preset threshold value, the solenoid is excited to open the solenoid valve 16 and the motor 13 is operated by the control unit 12 to drive the pump 15, and the urea is discharged from the addition nozzle 4. The ability to spray water U,
e. A function of correcting the addition amount of urea water U according to the NOx concentration near the exhaust outlet of the casing 3 obtained by the NOx concentration sensor 18 or the NOx concentration near the upstream of the addition nozzle 4 obtained by the NOx concentration sensor 28;
Etc.

  That is, the urea water U used for the NOx reduction treatment is actively heated by the heater 24, whereby decomposition of the urea water is promoted.

  That is, in the exhaust emission control device shown in FIG. 3, immediately after the engine 6 is started, the exhaust inlet of the casing 3 (exhaust G progress of the reduction catalyst 1 progresses by operating the vehicle in a cold region, continuing the low load operation of the engine 6, etc. Even when the ambient temperature on the upstream side in the direction does not increase, the amount of ammonia produced is ensured, and NOx contained in the exhaust G can be reduced efficiently.

  The relationship between the atmospheric temperature of the reduction catalyst 1 and the NOx reduction rate of the exhaust G in this embodiment has a tendency as shown by a solid line in FIG. 4, and the atmospheric temperature of the reduction catalyst 1 in the conventional example of FIG. The relationship with the NOx reduction rate has a tendency as shown by a broken line in FIG.

  FIG. 5 shows a third example of the embodiment of the exhaust gas purification apparatus of the present invention. In the figure, the parts denoted by the same reference numerals as those in FIGS. 1, 3, and 6 represent the same items. .

  In this exhaust purification apparatus, urea water U heated by a heater 24 is fed to the addition nozzle 22 attached to the exhaust manifold 7 of the engine 6.

  That is, the urea water U used for the NOx reduction treatment is sprayed on the high-temperature exhaust G immediately after being discharged from the cylinder of the engine 6, and when the exhaust G rotates the turbine 9, the urea Decomposition of urea water is promoted by the synergistic effect of the mixing of the fine droplets of water U and the exhaust G, and the temperature of the urea water U is positively raised by the heater 24.

  That is, in the exhaust emission control device shown in FIG. 5, immediately after the engine 6 is started, the exhaust inlet of the casing 3 (exhaust G progress of the reduction catalyst 1 progresses by operating the vehicle in a cold region, continuing the low load operation of the engine 6, etc. Even when the ambient temperature on the upstream side in the direction does not increase, the amount of ammonia produced is ensured, and NOx contained in the exhaust G can be reduced efficiently.

  It should be noted that the exhaust emission control device of the present invention is not limited to the embodiment described above, and it is needless to say that changes can be made without departing from the scope of the present invention.

  The exhaust emission control device of the present invention can be applied to various internal combustion engines including a diesel engine for vehicles.

It is a conceptual diagram which shows the 1st example of embodiment of the exhaust gas purification apparatus of this invention. It is a diagram which shows the relationship between the atmospheric temperature of a reduction catalyst, and the NOx reduction rate of exhaust. It is a conceptual diagram which shows the 2nd example of embodiment of the exhaust gas purification apparatus of this invention. It is a diagram which shows the relationship between the atmospheric temperature of a reduction catalyst, and the NOx reduction rate of exhaust. It is a conceptual diagram which shows the 3rd example of embodiment of the exhaust gas purification apparatus of this invention. It is a conceptual diagram which shows an example of the conventional exhaust gas purification apparatus.

Explanation of symbols

1 Urea selective reduction catalyst (NOx reduction catalyst)
2 Ammonia oxidation catalyst 4 Addition nozzle (reducing agent addition means)
6 Engine 8 Turbocharger 11 Distribution channel 22 Addition nozzle (reducing agent addition means)
24 Heater (heating means)
G exhaust U urea water

Claims (4)

  In the exhaust gas purification system in which the NOx reduction catalyst is installed in the exhaust flow path from the engine, the reducing agent addition means that mixes urea water in the exhaust is located upstream of the turbocharger attached to the engine in the exhaust traveling direction. An exhaust purification device characterized in that it is installed.   In an exhaust gas purification system that has a NOx reduction catalyst installed in the exhaust flow path from the engine, a reducing agent addition means that mixes urea water in the exhaust is located upstream of the reduction catalyst in the exhaust travel direction. And an exhaust emission control device provided with heating means for raising the temperature of urea water to be supplied to the reducing agent addition means.   In the exhaust gas purification device in which a NOx reduction catalyst is installed in the exhaust flow path from the engine, the reducing agent addition means for mixing urea water in the exhaust is located upstream of the turbocharger attached to the engine in the exhaust traveling direction. An exhaust emission control device provided with heating means for raising the temperature of urea water to be supplied to the reducing agent addition means.   The exhaust emission control device according to any one of claims 1 to 3, wherein an ammonia oxidation catalyst carrying a zeolite and a noble metal catalyst is installed on the downstream side of the NOx reduction catalyst.

Images